The compression encoding technologies are used for efficient transmission and storage of still pictures and video data. The systems of MPEG1 to MPEG4 and H.261 to H.264 are commonly used for video data.
A predictive coding system provides a method, device, and program for efficient encoding of mode information to identify the intra-frame prediction method of the target block even in the case where a larger number of prediction modes are provided in the method of generation of intra-frame predicted signals. To the predictive coding system further provides a method, device, and program for efficient decoding of encoded mode information.
The predictive coding system may perform an image predictive encoding method that includes: a region division step of partitioning an input picture into a plurality of blocks; a predicted signal generation step of determining, for pixel signals contained in a target block selected from a plurality of blocks, an optimum prediction mode with the smallest difference from among a plurality of prediction methods, and generating a prediction signal according to the optimum prediction signal, and generating a predicted signal in accordance with the optimum prediction mode; a residual signal generation step of obtaining a residual signal representing a difference between the pixel signal of the target block and the predicted signal; a signal encoding step of encoding the residual signal to generate a compressed signal; a prediction mode encoding step of encoding the optimum prediction mode; and a storage step of restoring the compressed signal and storing a restored signal as a reconstructed picture sample, or decoded signal, wherein the prediction mode encoding step includes: generating a candidate prediction mode list containing elements of optimum prediction modes of a plurality of previously-reproduced blocks neighboring the target block; encoding a flag to indicate whether the candidate prediction mode list contains an element corresponding to the optimum prediction mode; further encoding an index to the corresponding element in the candidate prediction mode list when there is a corresponding element; when there is no corresponding element, encoding with a number using the optimum prediction mode, after each element in the candidate prediction mode list is removed.
The predictive coding system may perform an image predictive decoding method that includes: an input step of accepting input of compressed picture data containing a residual signal and encoded information, the residual signal generated by dividing a picture into a plurality of blocks and performing predictive encoding of a target block, and the encoded information being about a prediction mode indicative of a generation method of a predicted signal of the target block; a restoration step of extracting the residual signal of the target block from the compressed picture data to restore a reproduced residual signal; a prediction mode decoding step of restoring the encoded information about the prediction mode to generate an optimum prediction mode; a predicted signal generation step of generating the predicted signal of the target block, the predicted signal generated based on the optimum prediction mode; a picture restoration step of adding the predicted signal to the reproduced residual signal to restore a pixel signal of the target block; and a storage step of storing the restored pixel signal as a reconstructed picture sample, or decoded signal, wherein the prediction mode decoding step includes: generating a candidate prediction mode list containing elements of optimum prediction modes of a plurality of previously-reproduced blocks neighboring the target block; decoding a flag to indicate whether the candidate prediction mode list contains an element corresponding to the optimum prediction mode; 1) when the flag indicates that “there is a corresponding element”, further decoding an index that indexes the candidate prediction mode list and defines an element indicated by the index as the optimum prediction mode; 2) when the flag indicates that “there is no corresponding element”, further decoding information about an REM mode and defining, as the optimum prediction mode, a value of the REM mode, which is converted based on the candidate prediction mode list.
In an embodiment, when the prediction mode information of the target block is encoded by performing intra-frame prediction using more intra-frame prediction modes than in the conventional technology, since the candidate prediction mode list consisting of a plurality of prediction modes is prepared, and an identifier of an element coincident with the prediction mode of the target block from the prepared candidate prediction mode list is encoded; the probability that the element is coincident with the prediction mode of the target block becomes higher, and thus the prediction mode information can be encoded by a smaller bit count. In other words, there is only one “most probable mode” in the conventional technology, whereas a plurality of “most probable modes” are prepared in the present invention; therefore, the present invention provides an effect of increasing the probability of occurrence of a “most probable mode” coincident with the prediction mode of the target block.
If the prediction mode of the target block is absent in the candidate prediction mode list, the prediction mode of the target block itself is encoded but, in that case, since a plurality of prediction modes in the candidate prediction mode list are excluded and new identification numbers are assigned to the remaining prediction modes, the prediction mode of the target block can be expressed by a smaller number, allowing encoding with a smaller bit length.
Namely, the predictive coding system provides an effect of enabling more efficient encoding of the information about the prediction mode in the case where the intra-frame prediction is carried out by more intra-frame prediction modes than in the conventional technology.
Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims.